The invention relates to fluid cushion ground effect vehicles and, specifically, to vehicles which derive their lift by dynamic action of an airfoil operating in close proximity to a surface plane. When conventional airfoils are operated in a region close to the ground plane, their normal pressure distribution is changed. Air is trapped, and pressure develops to a high level under the wing and adds this pressure to the lift of the airfoil. This added pressure of the trapped air on the bottom side of the wing is known as ground effect.
Ground Effect (GE) is encountered only when an airfoil aircraft is flying in close proximity to a flat ground plane. No one knows exactly what the altitude is, where you run out of GE and go into true flight, nor what effects varying wingspans have. The GE envelope is generally considered to be one quarter of the wing span or one and one third the wing chord for standard air craft designs. The ground effect principle increases the lifting capability of the wing up to 250% and promises an economical, fast, transport vehicle requiring minimum or no prepared special operating surfaces when operated as a large seaplane.
Ground Effect, unlike true flight, traps air between the airfoil/wing/vehicle and the ground/water surface and, thus, enhances the airfoil coefficient of Lift by 250 to 350 percent without increasing the aerodynamic drag factors. An airfoil flying in the GE envelope is much more efficient than an airfoil in true flight. An aircraft can operate in GE at one-quarter (1/4) the horsepower or one-quarter (1/4) the fuel consumption required for true flight. A trans-ocean cargo aircraft of comparable size and weight will burn four (4) times the fuel of a flying in GE aircraft.
High lift chambered airfoils (typical cargo aircraft) cannot safely remain in GE when the airspeed is sufficient to generate the lift required to fly. Flat/symmetrical airfoils only generate about two-thirds (2/3) the lift of a chambered airfoil; therefore, higher speeds can be attained in GE with the flat wing. In other words, the flat wing plane can remain at faster speeds for a longer time before encountering lifting forces that would force it into true flight. Flat/symmetrical airfoils have almost no Center of Lift travel like a chambered airfoil and have no pitch-up tendencies when entering and departing the GE envelope. An aircraft can fly in GE at about one-half (1/2) its minimum flight speed.
There have been several designs for the vehicles developed and tested since 1935. The tested vehicles have served to accumulate data on performance and have generally indicated:
1. It requires one-quarter to one-third the horsepower to fly in ground effect as it does in true flight.
2. That ground effect flight altitudes generally extend from ground level to about 25% of the aircraft wing span or 1.33 times the wing chord.
3. The vehicles are exceptionally smooth and stable on ground effect flight.
4. That low aspect ratio chamber wings (AR of slightly less and slightly larger than 1.0) tend to pitch up in transition from ground effect to true flight.
5. Have difficulty in maintaining ground effect flight when true flight speeds are reached.
6. Report poor turning capability while in ground effect flight, in that the vehicles must bank like an aircraft and may stick a wing in the water.
7. Large cargo versions of the aircraft type structures and plan-forms would be extremely expensive to build, have small cargo capacity for their size, and would not fit well into existing port and harbor facilities (long, thin docks).
8. The large and complex aircraft aluminum type structures and plan-forms would be short-lived operating in a sea environment due to corrosion, plus operating and maintenance costs would be excessive on these complex aluminum structures.
9. Industry proposals for ocean-going Wing In Ground Effect vehicles have not been for large vehicles, nor have they proposed anything except modified aircraft plan-forms and aircraft type construction.
10. Ocean-going Wing In Ground Effect vehicles must be large enough that their most economical cruising altitude clear all average sea-wave conditions. They must be large, long, and fast enough for the air cushion to average or cancel ocean wave and swell conditions. They must be able to land and take off in average sea conditions.
11. That large ocean-going vehicle structures should be sufficient to provide an adequate economical life span. Adequate flotation should be provided to prevent sinking in a down-at-sea condition with partial break-up.